Soil additives

ABSTRACT

A method of preparing a granulated soil additive of calcium sulfate and a soluble salt, preferably a fertilizer, which involves granulating the calcium sulfate employing the soluble salt, incorporated with the calcium sulfate in solution form, as the granulating agent.

United States Patent Wilson [451 May 2,1972

[54] SOIL ADDITIVES [21 Appl. No.: 888,868

[52] US. Cl ..71/34, 23/122, 23/313, 71/63, 71/64 D, 71/64 DA [51] Int. Cl. ..C05b 7/00, C05d 3/00 [58] Field of Search ..71/63, 64 D, 64 DA, 64 DC, 71/64 G, 34; 23/122, 313

[56] References Cited UNITED STATES PATENTS 1,548,358 8/1925 Edwards ..23/122 1,822,815 9/1931 Lichtenberger et al.. 1,973,473 9/1934 Edwards 2,792,295 5/1957 Wright ..71/64 G 2,893,858 7/1959 MacDonald et a1 ..71/64 DA 2.907,667 10/1959 Johnson ..23/122 X 2,913,308 11/1959 Dartey et al .....23/122 2,926,079 2/1960 Smith 71/64 DA 2,935,387 5/1960 Phillips ..71/64 DC 3,004,827 10/1961 Schaus... ...23/122 3,081,152 3/1963 Johnson. ..23/122 3,241,947 3/1966 Young ..71/63 X 3,326,633 6/1967 Carothers et al. ...23/122 3,334,988 8/1967 Newsom r ..71/63 3,480,387 11/1969 Yasutake et a1. ..23/122 FOREIGN PATENTS OR APPLICATIONS 743,867 10/1966 Canada ..23/122 802,105 12/1968 Canada ..23/122 208,779 3/1927 Great Britain. ..23/122 1,189,902 6/1967 Great Britain ..23/122 Primary Examiner-Reuben Friedman Assistant ExaminerRichard Barnes Attorney-Young and Quigg [5 7] ABSTRACT 3 Claims, No Drawings SOIL ADDITIVES This invention relates to soil additives. In one of its more specific aspects, this invention relates to granulated additives for soil improvement.

They are added to the gypsum in the form of a solution in any suitable solvent, preferably in the form of an aqueous solution, the solution preferably being at or near its saturation point in respect to the solubility of the granulating agent therein. The

The use of granulated fertilizers and the improvement obamount of solution sufficient to produce granulation is added tained upon their addition to the soil is well known. to the calcium sulfate, this amount generally being such as to Frequently, the addition to the soil of agents other than fertilform a we mixture comprising between about and about izers is desired. One of these which it is frequently desired to 25 Weight Percent Waler- IhaSmUCh as a principal Portion 0f dd i lf However, many f h forms i hi h lf the solvent is removed from the granules by evaporation. the could be added to the soil are insoluble in water and not readi- 10 Solution of the granulating agent can be added 10 the gyp m ly granulated by conventional methods. at or near the solutions boiling point. For example, aqueous One of the insoluble forms in which sulfur occurs in large solutions are generally added to the gypsum at temperatures quantities is by-product gypsum, or calcium sulfate produced, m about 170 F. to about 2l2 F. h for example, as the by pmduct from phosphoric acid produc 5 The solutlon of the granulating agent IS added to and mixed tion. However, because of the limited solubility of gypsum, it with h yp i y sultable "l l can be done by is not adaptable to granulation from aqueous solutions. While f g the 'f a f Ph of gyp the certain processes are directed to the production of granulated blmg b'emg ccfmlnued sfmable mlxmg results, after which fertilizer including gypsum, the method of this invention proi i-" 1S uced into granulat ng pp from vides an advance over the methods fd i so WhlCh 1t 15 recovered in desired granule sizes. Particles larger According to this invention there is provideda method f and smaller than desired can be reintroduced into the mixing preparinga granulated soil additive which comprises mixinga 1 Dl'ymg of the granules can be ie ut until the solution of the soluble salt with the calcium sulfate, granulat- P contains from f to about 3 Percent of Solvent in g the mixture, and recovering the granulated soil additive. based "P P h total welght of the granule- Accordingly, it is the object of this invention to provide an Tab]?! Indicates the results achieved when grahulafing 8Y1 improved so additive sum with various granulating agents employing the method It is another object of this invention to provide a novel ,descl'ibedruhder the cohditionsindicated- TABLE I I Granu- Product screen size, Water 111 m1x- Product, dry basis, wt. percent la 'ng wt. percent Run ture at granula- Other temp, No. Granulating agent tion, wt. percent inclusions Gypsum Additive Other F. +6 6+14 14 1 Fertilizer 18-46-0 17.1 o 85. 0 15.0 o 190 50. 6 43.1 6. 3 2 Ammonium nitrate 18.4 0 {)0 10 0 190 35.6 -16. 6 1T. 8 3 U 18.0 0 80 20 o 190 21.8 53, 6 6 1 Ammonium nitrate. 23.7 Limestone 7D. 1 i). 2 11.7 170 55. 2 21. 6 23. 2 5 Urea 14. 8 Limestone 72.0 18.0 10. 0 190 27.1 53. 7 19, 2 6.... Dinminoniuin phosphate" 18.0 0 80 2O 0 185 21. 6 22. 4 56.

*Connnvrcinl fertilizer, numerals denoting percentages of N, P20 and K 0.

method y which Sulfur Compounds can be made usable Soil- The data of Table l illustrate that a wide variety of granulatadditives.

The method of this invention produces hard, well-shaped granules of desirable size comprising gypsum and a soluble salt. Any soluble salt whose incorporation in the soil is unobjectionable can be employed as the granulating agent, although the use of materials commonly employed as fertil-- izers, for example, ammonium nitrate or diammonium phosphate, are preferably employed.

The solution of the granulating agent is mixed with the gypsum and the resulting mixture is granulated in conventional equipment while drying, auxiliary drying being employed as necessary to adjust the water content of the final product. Size separation and recycling of off-size granules to the granulation step can be employed.

The method of this invention contemplates the addition of the granulating solution to the gypsum, the gypsum preferably containing from about 15 to about 22 percent free water, preferably from about 17 to about 20 percent free water, the gypsum being wet as recovered from phosphoric acid production, or having had water added to its from an extraneous source. This gypsum can have contained in it quantities of phosphoric acid or solid extraneous materials such as limestone, carbon black, etc. Preferably, the gypsum will be in the form of a powder with about 70 percent having a Tyler Number of about -l00 and little, if any, having a Tyler Number greater than 20 mesh.

Any number of soluble salts can be employed as the granulating agent. Suitable salts are ammonium nitrate, ammonium phosphate, diammonium phosphate, urea, potash or suitable mixtures thereof, preferably as conventionally employed as commercial fertilizers. These granulating agents are added to the gypsum in amounts of from about 10 weight percent to about 30 weight percent of the weight of the final granule.

ing agents, including commercial fertilizers, can be employed and that extraneous particulate materials can be incorporated in the granules. ln all instances, granule hardness was equal to that of commercially acceptable fertilizers, being from about 0.3 to 1.5 psi, in some instances, being as high as 4.0 psi.

One of the prior art methods involves granulation of unwashed gypsum filter cake containing residual phosphoric acid using ammonium phosphate as the granulating agent. The ammonium phosphate is formed in situ by neutralizing the phosphoric acid with ammonia. A comparison of that method and that of the present invention illustrates the unexpected superior results of the method of the present invention.

For comparative purposes, the method of the present invention was carried out by adding diammonium phosphate in the form of an aqueous solution to a different sample of the same wet-process phosphoric acid gypsum cake. ln both'instances, the gypsum, after addition of the granulating agent and prior to granulating, contained substantially the same quantity of diammonium phosphate.

In both instances, the granulation and drying steps were substantially identical. However, as shown in the data of Table II, the method of this invention was unexpectedly superior'in respect to the properties of the granulated products.

TABLE II Method Component This Invention Prior Art Gypsum, Wt. Dry 65.4 65.4 85% H PQ, Present, g. 15.5 Ammonia Added, g. 0 3.4 Diammonium Phosphate Added, g. 16.6 0 Equivalent Diammonium Phosphate Added, g. 16.6 16.6 Water, g., Total 18.0 18.0

Granulated Product Properties pH 5.3 2.7 Screen Analysis, Tyler No. +6 21.6 (100% in 6 to +14 22.4 (form of 14 to +20 5.5 (1.5"to 2" -20 50.5 (diam. spheres.

In both instances, granulation was conducted at temperatures up to the maximum possible without the formation of an agglomerated mass. In the method of the present invention, a granulation temperature of about 180 F. was employed; in the prior art method, the maximum granulation temperature was limited to about 130 F.

It will be noted from the above that the method of this invention formed granules within those size ranges conventionally acceptable as commercial fertilizer. The prior art method, however, formed agglomerates, generally spheroidal, but of entirely unsatisfactory size for use as commercial fertilizer. The difference in pH values of the two granulated products is accountable by the fact that the formation of these large diameter particles in the prior art method prevented the thorough mixing and total neutralization of the ammonia with the acid on the gypsum and indicates a nonuniform product.

The method of this invention can employ any conventional apparatus for granulation such as pan granulators and drum granulators, the granulating agent additive being introduced into the granulator.

It will be evident from the foregoing that various modifications can be made to the method of this invention. Such, however, are considered as being within the scope of the invention.

What is claimed is:

1. A method of preparing a granulated soil additive which comprises a. introducing gypsum containing from about 15 to about 22 percent water into a granulator, about 70 weight percent of said gypsum having a Tyler number of about 1 00;

b. introducing into contact with said gypsum to form a wet mixture an aqueous solution of a salt, said solution being introduced in an amount sufficient to provide a salt content of from about 10 to about 30 weight percent of an after-defined, granulated soil additive, said wet mixture containing from about 15 to about 25 weight percent water;

c. granulating said mixture; and,

d. drying the granules at a temperature of about F. to produce a granulated soil additive containing from about 0.5 to about 3 weight percent water.

2. The method of claim 1 in which said salt is selected from the group consisting of ammonium nitrate, ammonium phosphate, diammonium phosphate, urea, potash and mixtures thereof.

3. The method of claim 1 in which said gypsum comprises unwashed gypsum containing phosphoric acid and said salt is diammonium phosphate. 

2. The method of claim 1 in which said salt is selected from the group consisting of ammonium nitrate, ammonium phosphate, diammonium phosphate, urea, potash and mixtures thereof.
 3. The method of claim 1 in which said gypsum comprises unwashed gypsum containing phosphoric acid and said salt is diammonium phosphate. 